The inventor of the present invention has been granted Letters Patent in Argentina under number 175,115 and the equivalent thereof in the United States under U.S. Pat. No. 3,640,107, directed to a key controlled lock having a locking bolt that is controlled by a key having a plurality of grooves of varied predetermined depths. The lock includes a fixed base having a channel defining on one side thereof, a keyway and at least three perforations that are defined non-linearly within the fixed base. The perforations open into the keyway and the channel is defined in the fixed base. A bolt control element is movable with respect to and is operatively connected to the bolt. The bolt control element is movably secured within the channel and has a plurality of bolt pin receiving bores which correspond to the plurality of perforations when the bolt control element is in the locked position. A plurality of bolt pins are slidably secured within the bores and a corresponding plurality of driver pins, having varied predetermined lengths are slidably secured within the perforations such that when the control element is locked, the bolt pins are depressed from the bores into the perforations and the driver pins are biased into contact with the surface of the keyway. When the key is inserted in the keyway, the plurality of grooves, of varied predetermined depths, in the key correspond with each of the driver pins, respectively. The plurality of grooves counterbias each of the driver pins and the bolt pins to cause each juncture between each of the bolt pins and the driver pins to be positioned at the interface of the bolt control element and the channel to allow the bolt control element to be moved in the channel without opposition from the bolt pins or the driver pins and without movement of the key.
The construction disclosed U.S. Pat. No. 3,640,107 allows the key to be withdrawn in three different positions of the portion which is movable with respect to the fixed one. This fact does not provide safety to users, as the key can be withdrawn in three different positions in which the locking mechanism will not be locked, providing a degree of insecurity which is not preferred in these kind of safety locks.
Further, the lock disclosed in U.S. Pat. No. 3,640,107, does not contemplate a mechanism that is provided with a joint bolt and latch, nor does it contemplate the system of an automatic closure of the bolt in the locking position without the need of using a key in the combination hub. Nor does this patent allow for the opening from the indoors by means of the simple operation of a control knob when the bolt is locked and kept in this position by the combination hub, and without using the key to release the combination hub.
On the other hand, in the disclosure U.S. Pat. No. 3,640,107 regarding the opening of the locking bolt, the combination hub actuating key is necessary from both the indoors and the outdoors. Such a difference is important regarding the present invention upon taking into account certain U.S. state provisions which require the use of doors provided with safety locks to be always permitted to be opened freely from indoors, that is, without the need of a key.